Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A method for producing a negative mold for casting a turbine blade with a
blade platform and at least one fastening element for fastening the
turbine blade to a blade fixture is provided. The surface of the
fastening element of a platform surface is located at a distance opposite
of the blade platform. A wax model of the turbine blade to be produced is
produced, a negative model of the turbine blade is created based on the
wax model after the wax model has hardened and the wax model is melted
out after completion of the negative mold. During hardening and/or during
storage and/or during transport of the wax model at least one spacer is
arranged between the platform surface of the blade platform and the
opposite surface of the fastening element of the wax model.

Claims:

1-8. (canceled)

9. A method for producing a negative mold for casting a turbine blade or
vane having a blade or vane platform and a fastening element for
fastening the turbine blade or vane to a blade or vane mount, comprising:
producing a wax model of the turbine blade or vane to be produced;
creating a negative mold of the turbine blade or vane on the basis of the
wax model once the wax model has hardened; melting out the wax model once
the negative mold has been completed; arranging a spacer between a
platform surface of the blade or vane platform and an opposite surface of
the fastening element of the wax model during storage and/or during
transport of the wax model; and removing the spacer from the wax model
before the negative mold is created, wherein the surface of the fastening
element is located opposite the platform surface of the blade or vane
platform at a distance.

10. The method as claimed in claim 9, wherein the spacer completely fills
a space between the platform surface of the blade or vane platform and
the opposite surface of the fastening element of the wax model.

11. The method as claimed in claim 9, wherein the spacer rests against a
further surface of the fastening element of the wax model.

12. The method as claimed in claim 9, wherein the spacer includes a
receptacle, matched to a shape of the fastening element of the wax model,
for receiving a part of the fastening element.

13. The method as claimed in claim 9, wherein the spacer is part of a
mold for producing the wax model.

14. The method as claimed in claim 9, wherein the spacer is made of
metal.

15. The method as claimed in claim 9, wherein the spacer is made of
ceramic.

16. A method for producing a turbine blade or vane having a blade or vane
platform and a fastening element for fastening the turbine blade or vane
to a blade or vane mount, comprising: providing a surface of the
fastening element located opposite a platform surface of the blade or
vane platform at a distance; and using a negative mold of the turbine
blade or vane to cast the turbine blade or vane, wherein the negative
mold of the turbine blade or vane is created as claimed in claim 9.

17. The method as claimed in claim 16, wherein the spacer completely
fills a space between the platform surface of the blade or vane platform
and the opposite surface of the fastening element of the wax model.

18. The method as claimed in claim 16, wherein the spacer rests against a
further surface of the fastening element of the wax model.

19. The method as claimed in claim 16, wherein the spacer includes a
receptacle, matched to a shape of the fastening element of the wax model,
for receiving a part of the fastening element.

20. The method as claimed in claim 16, wherein the spacer is part of a
mold for producing the wax model.

21. The method as claimed in claim 16, wherein the spacer is made of
metal.

22. The method as claimed in claim 16, wherein the spacer is made of
ceramic.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is the US National Stage of International
Application No. PCT/EP2010/054327, filed Mar. 31, 2010 and claims the
benefit thereof. The International Application claims the benefits of
European Patent Office application No. 09005327.3 EP filed Apr. 14, 2009.
All of the applications are incorporated by reference herein in their
entirety.

FIELD OF INVENTION

[0002] The present invention relates to a method for producing a negative
mold for casting a turbine blade or vane, in which method a wax model of
the turbine blade or vane is produced and the negative mold is created on
the basis of the wax model. In addition, the invention relates to an aid
used in the method and to a mold for producing a wax model of a turbine
blade or vane.

BACKGROUND OF INVENTION

[0003] By way of example, DE 197 26 111 C1 discloses a method for
producing a turbine rotor blade by casting, in which method a wax model
of the blade is produced, the blade root being produced by filling a
permanent mold having the blade contour. This is followed by the
production of a mold shell for casting the turbine blade, the permanent
mold remaining on the blade root. Once the wax model has been melted out,
the inner contour of the permanent mold defines the outer contour of the
turbine blade to be cast. In other words, the permanent mold represents
part of the casting mold for producing the turbine blade by casting.
Within the context of this method, the permanent mold should improve the
surface accuracy for shaping the blade root, such that complex reworking
of the blade root once the turbine blade has been cast is not necessary.
The permanent mold is either produced from an alloy material which is
resistant to high temperatures and has sufficient oxidation resistance,
such that it can be reused, or it is produced as a disposable permanent
mold made of a low-alloy steel.

SUMMARY OF INVENTION

[0004] With respect to this prior art, it is an object of the present
invention to provide an advantageous method for producing a negative mold
for casting a turbine blade or vane, with which method it is possible to
realize improved shaping even without the use of a permanent mold in
critical blade or vane regions.

[0005] It is a second object of the present invention to provide an
advantageous method for producing a turbine blade or vane, with which
method it is possible to achieve improved shaping of the turbine blade or
vane without the use of a permanent mold.

[0006] It is a further object of the present invention to provide an
advantageous aid for producing a negative mold of a turbine blade or
vane.

[0007] The first object is achieved by a method for producing a negative
mold for casting a turbine blade or vane as claimed in the claims, the
second object is achieved by a method for producing a turbine blade or
vane as claimed in the claims and the third object is achieved by a
spacer for a wax mold as claimed in the claims. The dependent claims
contain advantageous configurations of the invention.

[0008] In the method according to the invention for producing a negative
mold for casting a turbine blade or vane, the turbine blade or vane to be
cast has a blade or vane platform and a fastening element for fastening
the blade or vane to a blade or vane mount, wherein at least one surface
of the fastening element is located opposite a platform surface of the
blade or vane platform at a distance. In the method according to the
invention, a wax model of the turbine blade or vane to be produced is
produced, and a negative mold of the turbine blade or vane is created on
the basis of the wax model once the wax model has hardened. The wax model
is melted out once the negative mold has been completed. According to the
invention, during hardening and/or storage and/or transport of the wax
model, at least one spacer is arranged between the platform surface of
the blade or vane platform and the at least one opposite surface of the
fastening element of the wax model.

[0009] The invention is based on the knowledge that deviations in the
shaping in particular of the fastening elements of turbine blades or
vanes occur on account of deformations of the wax model during hardening
and/or storage up to the production of the negative mold and/or
transport. These deformations can be particularly serious in the region
of the blade or vane suspension, which is generally formed by hook-shaped
elements spaced apart from the blade or vane platform. However, these
hooks are particularly critical with respect to the dimensioning of the
distance between the hooks and the blade or vane platform. Specifically,
this distance defines the position of the platform in the hot gas path of
the turbine.

[0010] By using the spacer, it is possible for the particularly critical
distance between the hooks and the blade or vane platform to be kept
constant very effectively, and therefore reworking of a cast turbine
blade or vane is generally no longer necessary. Since the spacer is
removed from the wax model before the negative mold is produced, it does
not need to consist of a material which withstands the casting process
for casting the turbine blade or vane. Compared to the permanent mold
mentioned in the introduction, it is therefore possible to use a material
which is very much less resistant to high temperatures and therefore a
less expensive material.

[0011] It is advantageous if the spacer is arranged between the platform
surface of the blade or vane platform and the at least one opposite
surface of the fastening element as early as during the hardening of the
wax model, but also remains in the wax model until immediately before the
negative mold is produced. It is thereby possible for deformations of the
wax model which influence the distance between the blade or vane platform
and the fastening element to be avoided without interruption from
production up to the use thereof.

[0012] In order to distribute any forces which occur as uniformly as
possible, it is advantageous if the at least one spacer completely fills
the space between the platform surface of the blade or vane platform and
the at least one opposite surface of the fastening element.

[0013] In order to prevent not only displacements in the distance between
the fastening element and the blade or vane platform, but also lateral
movements between the blade or vane platform and the fastening element,
the spacer can rest against at least one further surface of the fastening
element. In addition, it is also possible to use a spacer which has a
receptacle, matched to the shape of the fastening element, for receiving
at least part of the fastening element. The fastening element can thereby
be secured against deformations in all relevant directions. In
particular, the spacer can also be part of a mold for producing the wax
model of the turbine blade or vane.

[0014] The spacer used can be produced, in particular, from metal or
ceramic. If the spacer is produced from metal, steel or aluminum are
suitable, for example, in which case aluminum involves advantages on
account of its low weight.

[0015] In the method according to the invention for producing a turbine
blade or vane, a turbine blade or vane having a blade or vane platform
and a fastening element for fastening the blade or vane to a blade or
vane mount is produced, wherein at least one surface of the fastening
element is located opposite a platform surface of the blade or vane
platform at a distance. The turbine blade or vane is cast with the aid of
a negative mold of the turbine blade or vane. According to the invention,
the negative mold is created according to the method according to the
invention for producing a negative mold.

[0016] The method according to the invention for producing a turbine blade
or vane makes it possible to produce the turbine blade or vane with
surfaces and dimensions which are readily controllable in the
particularly relevant regions of the suspension, without this requiring
the use of a permanent mold.

[0017] The invention also provides a spacer for a wax mold of a turbine
blade or vane having a blade or vane platform and a fastening element for
fastening the blade or vane to a blade or vane mount, wherein at least
one surface of the fastening element is located opposite a platform
surface of the blade or vane platform at a distance. The spacer according
to the invention has a receptacle, matched to the shape of the fastening
element, for receiving at least part of the fastening element. Within the
context of the method according to the invention for producing a negative
mold, such a spacer can advantageously be used for the production of a
turbine blade or vane. It can be produced, in particular, from metal, for
example from steel or aluminum. It can also be produced from ceramic.

[0018] A further aspect of the invention provides a mold for producing a
wax model of a turbine blade or vane. The mold comprises a removable or
detachable part which remains on the wax model as the wax model is being
removed from the mold and forms a spacer according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Further features, properties and advantages of the present
invention will become apparent from the following description of
exemplary embodiments with reference to the accompanying figures.

[0021]FIG. 2 shows a perspective view of an example of a turbine blade or
vane.

[0022]FIG. 3 shows an example of a combustion chamber of a gas turbine.

[0023]FIG. 4 shows a highly diagrammatic view of the suspension of a
turbine blade or vane.

[0024]FIG. 5 shows the sequence of a method for producing a turbine blade
or vane by casting.

[0025]FIG. 6 shows a section of a wax model of a turbine blade or vane.

DETAILED DESCRIPTION OF INVENTION

[0026]FIG. 1 shows, by way of example, a partial longitudinal section
through a gas turbine 100.

[0027] In the interior, the gas turbine 100 has a rotor 103 with a shaft
101 which is mounted such that it can rotate about an axis of rotation
102 and is also referred to as the turbine rotor.

[0028] An intake housing 104, a compressor 105, a, for example, toroidal
combustion chamber 110, in particular an annular combustion chamber, with
a plurality of coaxially arranged burners 107, a turbine 108 and the
exhaust-gas housing 109 follow one another along the rotor 103.

[0029] The annular combustion chamber 110 is in communication with a, for
example, annular hot-gas passage 111, where, by way of example, four
successive turbine stages 112 form the turbine 108.

[0030] Each turbine stage 112 is formed, for example, from two blade or
vane rings. As seen in the direction of flow of a working medium 113, in
the hot-gas passage 111 a row of guide vanes 115 is followed by a row 125
formed from rotor blades 120.

[0031] The guide vanes 130 are secured to an inner housing 138 of a stator
143, whereas the rotor blades 120 of a row 125 are fitted to the rotor
103 for example by means of a turbine disk 133.

[0032] A generator (not shown) is coupled to the rotor 103.

[0033] While the gas turbine 100 is operating, the compressor 105 sucks in
air 135 through the intake housing 104 and compresses it. The compressed
air provided at the turbine-side end of the compressor 105 is passed to
the burners 107, where it is mixed with a fuel. The mix is then burnt in
the combustion chamber 110, forming the working medium 113. From there,
the working medium 113 flows along the hot-gas passage 111 past the guide
vanes 130 and the rotor blades 120. The working medium 113 is expanded at
the rotor blades 120, transferring its momentum, so that the rotor blades
120 drive the rotor 103 and the latter in turn drives the generator
coupled to it.

[0034] While the gas turbine 100 is operating, the components which are
exposed to the hot working medium 113 are subject to thermal stresses.
The guide vanes 130 and rotor blades 120 of the first turbine stage 112,
as seen in the direction of flow of the working medium 113, together with
the heat shield elements which line the annular combustion chamber 110,
are subject to the highest thermal stresses.

[0035] To be able to withstand the temperatures which prevail there, they
may be cooled by means of a coolant.

[0036] Substrates of the components may likewise have a directional
structure, i.e. they are in single-crystal form (SX structure) or have
only longitudinally oriented grains (DS structure).

[0037] By way of example, iron-based, nickel-based or cobalt-based
superalloys are used as material for the components, in particular for
the turbine blade or vane 120, 130 and components of the combustion
chamber 110.

[0038] Superalloys of this type are known, for example, from EP 1 204 776
B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949; these
documents form part of the disclosure with respect to the chemical
composition of the alloys.

[0040] It is also possible for a thermal barrier coating to be present on
the MCrAlX, consisting for example of ZrO2,
Y2O3--ZrO2, i.e. unstabilized, partially stabilized or
fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium
oxide.

[0041] Columnar grains are produced in the thermal barrier coating by
suitable coating processes, such as for example electron beam physical
vapor deposition (EB-PVD).

[0042] The guide vane 130 has a guide vane root (not shown here), which
faces the inner housing 138 of the turbine 108, and a guide vane head
which is at the opposite end from the guide vane root. The guide vane
head faces the rotor 103 and is fixed to a securing ring 140 of the
stator 143.

[0043]FIG. 2 shows a perspective view of a rotor blade 120 or guide vane
130 of a turbomachine, which extends along a longitudinal axis 121.

[0044] The turbomachine may be a gas turbine of an aircraft or of a power
plant for generating electricity, a steam turbine or a compressor.

[0045] The blade or vane 120, 130 has, in succession along the
longitudinal axis 121, a securing region 400, an adjoining blade or vane
platform 403 and a main blade or vane part 406 and a blade or vane tip
415.

[0046] As a guide vane 130, the vane 130 may have a further platform (not
shown) at its vane tip 415.

[0047] A blade or vane root 183, which is used to secure the rotor blades
120, 130 to a shaft or a disk (not shown), is formed in the securing
region 400.

[0048] The blade or vane root 183 is designed, for example, in hammerhead
form. Other configurations, such as a fir-tree or dovetail root, are
possible.

[0049] The blade or vane 120, 130 has a leading edge 409 and a trailing
edge 412 for a medium which flows past the main blade or vane part 406.

[0050] In the case of conventional blades or vanes 120, 130, by way of
example solid metallic materials, in particular superalloys, are used in
all regions 400, 403, 406 of the blade or vane 120, 130.

[0052] The blade or vane 120, 130 may in this case be produced by a
casting process, by means of directional solidification, by a forging
process, by a milling process or combinations thereof.

[0053] Workpieces with a single-crystal structure or structures are used
as components for machines which, in operation, are exposed to high
mechanical, thermal and/or chemical stresses.

[0054] Single-crystal workpieces of this type are produced, for example,
by directional solidification from the melt. This involves casting
processes in which the liquid metallic alloy solidifies to form the
single-crystal structure, i.e. the single-crystal workpiece, or
solidifies directionally.

[0055] In this case, dendritic crystals are oriented along the direction
of heat flow and form either a columnar crystalline grain structure (i.e.
grains which run over the entire length of the workpiece and are referred
to here, in accordance with the language customarily used, as
directionally solidified) or a single-crystal structure, i.e. the entire
workpiece consists of one single crystal. In these processes, a
transition to globular (polycrystalline) solidification needs to be
avoided, since non-directional growth inevitably forms transverse and
longitudinal grain boundaries, which negate the favorable properties of
the directionally solidified or single-crystal component.

[0056] Where the text refers in general terms to directionally solidified
microstructures, this is to be understood as meaning both single
crystals, which do not have any grain boundaries or at most have
small-angle grain boundaries, and columnar crystal structures, which do
have grain boundaries running in the longitudinal direction but do not
have any transverse grain boundaries. This second form of crystalline
structures is also described as directionally solidified microstructures
(directionally solidified structures).

[0057] Processes of this type are known from U.S. Pat. No. 6,024,792 and
EP 0 892 090 A1;these documents form part of the disclosure with respect
to the solidification process.

[0058] The blades or vanes 120, 130 may likewise have coatings protecting
against corrosion or oxidation e.g. (MCrAlX; M is at least one element
selected from the group consisting of iron (Fe), cobalt (Co), nickel
(Ni), X is an active element and stands for yttrium (Y) and/or silicon
and/or at least one rare earth element, or hafnium (Hf)). Alloys of this
type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or
EP 1 306 454 A1, which are intended to form part of this disclosure with
respect to the chemical composition of the alloy.

[0059] The density is preferably 95% of the theoretical density.

[0060] A protective aluminum oxide layer (TGO=thermally grown oxide layer)
is formed on the MCrAlX layer (as an intermediate layer or as the
outermost layer).

[0061] The layer preferably has a composition Co-30Ni-28Cr-8Al-0.6Y-0.7Si
or Co-28Ni-24Cr-10Al-0.6Y. In addition to these cobalt-based protective
coatings, it is also preferable to use nickel-based protective layers,
such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or
Ni-25Co-17Cr-10Al-0.4Y-1.5Re.

[0062] It is also possible for a thermal barrier coating, which is
preferably the outermost layer and consists for example of ZrO2,
Y2O3--ZrO2, i.e. unstabilized, partially stabilized or
fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium
oxide, to be present on the MCrAlX.

[0063] The thermal barrier coating covers the entire MCrAlX layer.

[0064] Columnar grains are produced in the thermal barrier coating by
suitable coating processes, such as for example electron beam physical
vapor deposition (EB-PVD).

[0065] Other coating processes are possible, for example atmospheric
plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may
include grains that are porous or have micro-cracks or macro-cracks, in
order to improve the resistance to thermal shocks. The thermal barrier
coating is therefore preferably more porous than the MCrAlX layer.

[0066] Refurbishment means that after they have been used, protective
layers may have to be removed from components 120, 130 (e.g. by
sand-blasting). Then, the corrosion and/or oxidation layers and products
are removed. If appropriate, cracks in the component 120, 130 are also
repaired. This is followed by recoating of the component 120, 130, after
which the component 120, 130 can be reused.

[0067] The blade or vane 120, 130 may be hollow or solid in form. If the
blade or vane 120, 130 is to be cooled, it is hollow and may also have
film-cooling holes 418 (indicated by dashed lines).

[0068]FIG. 3 shows a combustion chamber 110 of a gas turbine. The
combustion chamber 110 is configured, for example, as what is known as an
annular combustion chamber, in which a multiplicity of burners 107, which
generate flames 156, arranged circumferentially around an axis of
rotation 102 open out into a common combustion chamber space 154. For
this purpose, the combustion chamber 110 overall is of annular
configuration positioned around the axis of rotation 102.

[0069] To achieve a relatively high efficiency, the combustion chamber 110
is designed for a relatively high temperature of the working medium M of
approximately 1000° C. to 1600° C. To allow a relatively
long service life even with these operating parameters, which are
unfavorable for the materials, the combustion chamber wall 153 is
provided, on its side which faces the working medium M, with an inner
lining formed from heat shield elements 155.

[0070] On the working medium side, each heat shield element 155 made from
an alloy is equipped with a particularly heat-resistant protective layer
(MCrAlX layer and/or ceramic coating) or is made from material that is
able to withstand high temperatures (solid ceramic bricks).

[0071] These protective layers may be similar to the turbine blades or
vanes, i.e. for example MCrAlX: M is at least one element selected from
the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an
active element and stands for yttrium (Y) and/or silicon and/or at least
one rare earth element or hafnium (Hf). Alloys of this type are known
from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454
A1.

[0072] It is also possible for a, for example, ceramic thermal barrier
coating to be present on the MCrAlX, consisting for example of ZrO2,
Y2O3--ZrO2, i.e. unstabilized, partially stabilized or
fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium
oxide.

[0073] Columnar grains are produced in the thermal barrier coating by
suitable coating processes, such as for example electron beam physical
vapor deposition (EB-PVD).

[0074] Other coating processes are possible, e.g. atmospheric plasma
spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may include
grains that are porous or have micro-cracks or macro-cracks, in order to
improve the resistance to thermal shocks.

[0075] Refurbishment means that after they have been used, protective
layers may have to be removed from heat shield elements 155 (e.g. by
sand-blasting).

[0076] Then, the corrosion and/or oxidation layers and products are
removed. If appropriate, cracks in the heat shield element 155 are also
repaired. This is followed by recoating of the heat shield elements 155,
after which the heat shield elements 155 can be reused.

[0077] Moreover, a cooling system may be provided for the heat shield
elements 155 and/or their holding elements, on account of the high
temperatures in the interior of the combustion chamber 110. The heat
shield elements 155 are then, for example, hollow and may also have
cooling holes (not shown) opening out into the combustion chamber space
154.

[0078]FIG. 4 shows a highly diagrammatic illustration of the suspension
of a guide vane 1 on a holding ring 3, which extends in the
circumferential direction of the turbine at least around part of the
circumference. The holding element 3 has holding projections 5, on which
the turbine blade or vane 1 is fastened.

[0079] The turbine blade or vane 1 has a main blade or vane part 9 and at
least one blade or vane platform 11 arranged at the radially outer end of
the main blade or vane part 9. A corresponding blade or vane platform can
also be arranged at the radially inner end of the main blade or vane part
9 (not shown in FIG. 4). The blade or vane platform 11 has a radially
inner platform surface 13, which forms part of the wall of the flow path
for the hot combustion gases in the gas turbine. Holding hooks 7 are
foamed on the radially outer platform surface 15 located opposite the
radially inner platform surface 13 and can be used to suspend the turbine
blade or vane on the holding projections 5 of the holding element 3.
Corresponding holding hooks can also be present on the radially inner
platform.

[0080] In combination with the position of the holding projections 5 of
the holding element 3, the distance d between the radially outer platform
surface 15 and a hook surface 17 located opposite this platform surface
determines the positioning of the radially inner platform surface 13 in
the hot gas path of the gas turbine, and is therefore of great importance
for the formation of a hot gas path which is optimized in terms of flow.
Within the context of the production of a turbine blade or vane by
casting, it is therefore of great importance to ensure a defined distance
d between the radially outer platform surface and the hook surface 7.

[0081] A method for producing the turbine blade or vane shown in FIG. 4 by
casting is described below with reference to FIG. 5.

[0082] In a first method step 19, a casting mold is created for a wax
model of the turbine blade or vane 9 to be produced. Since no
particularly high temperatures prevail during casting of the wax model,
the material for the wax model casting mold can be selected so that it is
optimized in terms of processability, such that the contour of the wax
model can be produced precisely as a negative mold. A casting mold once
produced for the wax model can also be reused, and therefore the step of
producing a casting mold for a wax model does not necessarily have to be
present in each method for producing a negative model for a turbine blade
or vane. Only when a turbine blade or vane with a new geometry is to be
produced for the first time is it necessary to produce a new casting mold
for the corresponding wax model.

[0083] In step 21, the wax model of the turbine blade or vane is cast by
means of the casting mold for the wax model. Once the wax model has
hardened to such an extent that the casting mold can be removed, spacer
elements are inserted into the region of the holding hooks 7 in step 23.
Such a spacer element 219 is shown schematically in FIG. 6. The figure
shows a section of a wax model 201 of the turbine blade or vane 1 shown
in FIG. 4. The wax model has a model main blade or vane part 209, a model
platform 211 with a radially inner model platform surface 213 and a
radially outer model platform surface 215. A model holding hook 207
extends from the model platform 211 and has a model hook surface 217
which faces toward the outer model platform surface 215 and is spaced
apart therefrom.

[0084] As soon as the wax model 209 can be taken from the mold, spacer
elements 219 are pushed into the intermediate space between the radially
outer model platform surface 215 and the opposite model hook surface 217.
The spacer 219 is produced from a dimensionally stable material, for
example metal or ceramic. Metallic materials in particular, for instance
steel or aluminum, can be produced with precise dimensions, such that the
thickness of the spacer can be matched very accurately to the distance d
to be observed between the radially outer model platform surface 215 and
the opposite model hook surface 217.

[0085] As soon as the spacer 219 has been pushed into the intermediate
space between the radially outer platform surface 215 and the opposite
model hook surface 217, the distance between these two surfaces is
secured against a change on account of deformations in the wax model
during further hardening and/or during transport and/or storage of the
wax model. The spacer 219 additionally has a thickened portion 221, which
serves as an edge located opposite the end face 223 of the model hook
207. It is thereby also possible to reliably counteract displacement of
the end face 223 by deformation, in particular, of the model hook 207.

[0086] Even though the spacer 219, in the present exemplary embodiment, is
inserted after the wax model has been removed from the casting mold, the
spacer can also be designed such that, during the casting process, it
forms part of the casting mold which can subsequently be taken from the
casting mold together with the wax model or can be separated from the
casting mold. Since, in this alternative configuration of the method, the
spacer is already located in its position during casting, in the region
of the model hook 207 the wax model is also secured against deformations
which might occur as the model is being removed from the mold.

[0087] The spacer 229 advantageously remains in the wax model 201 of the
turbine blade or vane 1 until a negative mold is created for the turbine
blade or vane 1 on the basis of the wax model 201. Once the spacer has
been removed in step 25 of the method, the negative mold is formed around
the wax model, for example by means of a ceramic material (step 27). Once
the negative mold has set, the wax is melted out of the negative mold,
and therefore the cavity thereby created is available for casting the
turbine blade or vane in step 29. Once the turbine blade or vane has been
cast with the aid of the negative mold, the negative mold is removed and
the method for producing the turbine blade or vane is complete.

[0088] The present invention provides a simple means with which it is
possible to counteract deformation of the wax model used during a casting
process for producing a turbine blade or vane. It is thereby possible to
achieve improvements in the observance of a precise geometry of the wax
model, as a result of which it is possible to reduce the number of
erroneously cast turbine blades or vanes, which are to be reworked or, in
the worst case, represent rejects.